1. Field of the invention
The present invention relates to methods of forming dielectric materials and, more particularly to methods of forming nitrogen-rich silicon oxide-based dielectric materials for use in semiconductor integrated circuit devices.
2. Description of Related Art
As integrated circuit (IC) devices become more advanced to provide enhanced functionality, higher speeds and lower voltage operation, the number of circuit elements per IC generally increases while the allowable area of each of those elements is reduced. While this downward scaling process most obviously involves reducing lateral dimensions, the vertical dimensions of some circuit elements, e.g. gate dielectric film thicknesses, must also be reduced. Thus for a typical high performance transistor with a gate length less than 0.25 micron (xcexcm), gate dielectric layer thickness will typically be less than 5 nanometers (nm).
Unfortunately, where these thin gate dielectric layers are silicon oxide, some commonly employed dopants can readily diffuse through the layer and impact device performance. For example, in dual poly CMOS technology, boron from a boron doped P-type polysilicon gate electrode can readily diffuse through a conventional silicon oxide gate dielectric and into the underlying N-type channel region. Thus the surface carrier concentration of the underlying region is changed and the threshold voltage (Vth) degraded. In addition to Vth degradation, the susceptibility of thin silicon oxide dielectrics to diffusion of dopants can also lead to other device performance problems. For example, degradation of dielectric integrity and hot carrier resistance.
Nitrogen-rich or nitrided silicon oxide films can provide a barrier to diffusion of dopants such as boron. Hence Vth degradation of transistors formed using nitrogen-rich silicon oxide gate dielectrics is reduced. Additionally, such nitrided silicon oxide films have improved hot carrier resistance and dielectric integrity. However, the formation of such films with sufficient peak nitrogen concentration has been problematic.
One previously known method for forming nitrogen-rich silicon oxide films with sufficient peak nitrogen concentration employs ammonia (NH3) nitridization of silicon oxide films at temperatures between 900 and 1200 degrees Celsius (xc2x0 C.). However, such films are also hydrogen rich making the films unsuitable for use as gate dielectrics in MOSFETs without additional processing to reduce hydrogen content. Another solution to the hydrogen problem is to avoid its inclusion during film formation. To this effect, the use of nitrous oxide (N2O) for direct oxynitridization or nitridization of silicon oxide films has been reported. However, the reported methods seem to require temperatures approaching 1000xc2x0 C. or a film thickness in excess of 5 nm to provide sufficient peak nitrogen concentration for the film act as a diffusion barrier. Unfortunately, the high temperature processing required to form thin films can result in dopant redistribution and shifts in Vth. Where Rapid Thermal Processing (RTP) systems are used to limit time at temperature and thus reduce dopant redistribution, film uniformity has been reported to be problematic.
Also known to avoid the inclusion of hydrogen is the use of nitric oxide (NO) for direct oxynitridization or nitridization of silicon oxide films. Advantageously, some reports indicate that films formed using NO have higher peak nitrogen concentration than N2O formed films for any given process temperature. For example, Z. Q. Yao, et al. (xe2x80x9cHigh quality ultathin dielectric films grown on silicon in a nitric oxide ambientxe2x80x9d, Appl. Phys. Lett., vol. 64 (26), June, 1994, pp. 3584-3586), report that for films formed using RTP systems at 1150xc2x0 C., the film formed using NO had a peak nitrogen concentration approximately three times greater than the film formed using N2O (4.4% versus 1.4%). However, while peak nitrogen concentration is high, the growth rate of the films formed using NO is slow and self-limiting making its use problematic.
Thus it would be advantageous to have methods for forming nitrogen-rich silicon oxide films at acceptable growth rates and with acceptable uniformity for use in high performance IC devices without resorting to high temperature processing. It would also be advantageous for such methods to provide thin nitrogen-rich silicon oxide films having a sufficiently high nitrogen concentration to provide enhanced resistance to dopant that avoid the problems of previously known methods. Furthermore, it would be advantageous for such methods to employ well known reagents and equipment thus providing safe, cost-effective wafer processing. Finally, it would also be advantageous to have IC structures and devices that realize the full benefit of both lateral and vertical scaling while having enhanced resistance to Vth degradation due to dopant diffusion through gate dielectric layers.
In accordance with the present invention, methods for forming nitrogen-rich silicon oxide films and the structures and IC""s formed thereby, are provided. In some embodiments of the present invention an apparatus for forming a nitrogen-rich silicon oxide film is provided, the apparatus having at least two fluidically coupled zones or chambers. In some embodiments, a first chamber or zone is commonly referred to as a torch zone or torch chamber and a second chamber is commonly referred to as a process zone or process chamber.
Some methods in accordance with embodiments of the present invention provide for the formation of a first silicon oxide film by positioning silicon wafers or other suitable semiconductor substrates in the process chamber of the apparatus and providing an oxidizing atmosphere to that chamber. In some embodiments the atmosphere provided is a dry oxidizing atmosphere while in other embodiments the atmosphere provided is a wet oxidizing atmosphere.
Methods in accordance with embodiments of the present invention also encompass the formation of a nitrogen-rich silicon oxide film by providing a nitridizing atmosphere to the silicon wafers. The term xe2x80x9cnitrogen-richxe2x80x9d is understood to mean a peak nitrogen concentration of between approximately 0.5 to 3.5 atomic percent (at %) or higher. In addition, the term xe2x80x9cnitridizing atmospherexe2x80x9d is understood to mean an atmosphere that provides for the formation of nitrogen-rich silicon oxide films. In some embodiments providing the nitridizing atmosphere to the silicon wafers encompasses introducing nitrous oxide (N2O) into the torch region at a first temperature. Advantageously, this first temperature is selected to be sufficiently high to promote an exothermic reaction which forms the nitridizing atmosphere. Subsequently the atmosphere formed is directed to the silicon wafers in the process chamber through the fluidic coupling between the chambers.
Embodiments of the present invention also include semiconductor devices and integrated circuits that incorporate nitrogen-rich silicon oxide films formed by methods in accordance with the present invention. For example, such semiconductor devices embodiments encompass devices that employ nitrogen-rich gate dielectric films, tunnel dielectrics or gate sidewall dielectrics formed using the methods of the present invention.